Red Bull driver Sergio Perez is keeping his feet firmly on the ground after setting the pace in Friday practice for the United States Grand Prix, describing rival team Mercedes as "very strong".
Mercedes dominated first practice at the Circuit of the Americas, with Valtteri Bottas and Lewis Hamilton almost a full second quicker than Perez's teammate, Max Verstappen, as details of a 'trick' ride height system emerged.
Mercedes' rivals closed in during FP2, with Perez leading the way from McLaren's Lando Norris, though Hamilton had his best lap time deleted for exceeding track limits, an effort that would have been a tenth faster.
Perez described a "good day" for himself and Red Bull but admits that improvements are needed in terms of both one-lap pace and longer runs if they are to take the fight to Mercedes as the weekend develops.
"Obviously, it's gonna be very tight," said Perez on Friday afternoon.
"It's all about tomorrow, Saturday, trying to put it all together, and trying to find those couple of things that put us in the mix for pole.
"It was a promising FP2, but yeah, there's a lot to be done to try to improve the car. I also feel that there is so much to still improve [on] our long run pace.
"I wasn't very happy with my tyre deg, so I think there's room to improve there and try to find a bit more pace.
"All in all, I think it's a positive Friday, but we'll see tomorrow where we end up."
Asked specifically about Mercedes, and the significant gap they held over the field in FP1, Perez said: "They were certainly very strong... very strong today, so we'll see what they have for tomorrow."